The new concept has been received extremely well, and Nigel Lock from Groveley Detection explains that this ultrasonic detector – Incus – detects the sound that a gas leak makes. “It doesn’t differentiate between gases, it just detects the ultrasonic waves created by a leak as gas migrates from high pressure to low pressure (minimum pressure needs to be 2 BarA), and is therefore suitable for flammable as well as toxic gas detection.

“With conventional systems, the actual detector has to be placed in the vapour cloud, but the GDU Incus doesn’t require this, because it is ‘hearing’ and not actually ‘seeing’,” he explains.

Groveley’s new detector is unaffected by wind direction or weather, as it just senses changes in pressure all around itself, listening for a gas cloud. Lock adds that according to the UK Health and Safety Executive, currently 35 per cent of all offshore gas leaks are not picked up by conventional detection systems. He hopes to fill that gap with the Incus, but emphasizes that Grovely wants this detector to work in combination with other types of detection equipment and not as a substitute. “There has to be a staged approach, and the Incus is a first stage detector. It detects that a gas leak is present and then the other equipment – point and open path detection – should identify the type of gas and the volume.”

The GDU Incus uses a Piezo sensor which is encapsulated in a ceramic case so it doesn’t age. Neither does it need calibrating in the field because the detector is set up in the factory, therefore requiring less maintenance.

It even comprises an automatic self cleaning system that protects it from damaging influences in dusty, dirty or other harsh environments. When the sensor gets dirty, it blasts compressed air accross the front of the detector until it is clean. In addition, it is also able to cope with temperature extremes, because it features a heating and cooling system. As a result it is suitable for use all over the world and some versions can operate in temperatures from -50 degrees C to +50 degrees C.

Lock sees great potential for this detector on platforms in older gas fields, which are now turning sour, meaning that levels of hydrogen sulphide are present. The reinjection system that most gas platforms use inserts water and sludge back into a well, thus creating the right conditions for the bacteria that produce this toxic gas.
The main problem with hydrogen sulphide is that olfactory amnesia occurs after certain levels of H2S are released, says Lock, so that the nose doesn’t detect the smell any more.

It is possible to smell small amounts of the agent – it smells like rotten eggs – but when a big cloud comes along, the nose shuts off. This is just one of the reasons why having a certified detection system is so important.

“When it comes to certification, you want to make sure that equipment is not going to cause a problem, and that is why the Incus is currently going through all the certification procedures. This detector is going to be certified as flameproof, and this means that this piece of kit can be installed in an area where flammable gas is present.”

As well as getting ATEX certification (European approval) Groveley is aiming to market this ultrasonic detector on an international level, including in the Middle East where they tend often to focus on US regulations. This is the reason why it is currently also trying to gain FM and UL approvals as well as complying with IECEX (an international safety standard for electronic equipment).

Groveley is looking to comply with all relevant standards, and because the Incus is a critical safety piece of equipment, the company is expecting the ultrasonic detector to be rated under a Safety Integrity Level (SIL) of 3. Safety integrity levels range from one to four, each corresponding to a likelihood of failures of a safety function.

Interoperability is not an issue either because the Incus slots on to any control hardware. In addition, the detector also features an auto test function that can either be initiated at will, or set to test itself periodically, and therefore the cost of ownership is low. “And this is exactly what operators are looking for, as there are fewer people available on rigs these days to carry out maintenance.”

Visitors to the Offshore North Sea 2008 exhibition responded very well to the Incus, says Lock. “It is a new technology to some people and everyone was very interested. The responses from every engineer we talked with were very positive. We spent two years developing the Incus and we believe it is a good product, and ONS showed us that the market is ready for it.”

ONS is only the first stage of the GDU Incus’ launch cycle, and Groveley is testing the market to gauge the response. It will finalise the design based on that feedback, and production of the new detector is expected to start in January 2009.

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